Electrodeposition of copper



United States Patent 'Ofilice 2,841,542 ELECTRODEPOSITION OF COPPER John W. Manquen, Berkley, Mich., assignor to The Udylite Research Corporation, Detroit, Mich., a cor-' poration of Michigan No Drawing. Application December 19, 1955 Serial No. 553,717 16 Claims. (Cl. 204-52) This invention relates to the electrodeposition of copper from aqueous alkaline cyanide solutions. More particularly this invention concerns the electrodeposition of bright fine-grained deposits of copper from aqueous alkaline cyanide solutions over widecurrent density ranges.

In accordance with this invention it has been found that the addition of small quantities of tellurium to copper cyanide baths having a remarkably wide range of composition makes possible a marked increase in luster and brightness of the copper deposit which is obtained upon electrolysis of such baths, the best results being obtained when the cathode efiiciency is less than 100%. The tellurium may be added in the form of tellurites, tellurides, tellurates or telluric compounds. It is preferred to introduce tellurium into the bath in the form of tellurium oxide (TeO dissolved in asolution of an alkali such as sodium or potassium hydroxide with or without Rochelle salts, glyco lates, gluconates or citrates, but other hydroxides or solvents may be used to disperse the tellurium oxide.

The optimum concentration of tellurum in the bath is in the range of about 0.0002 gram per liter to about 0.006 gram per liter. As used in this specification and in the appended claims the quantities given for tellurium refer to quantities calculated as the metal. An excess above about 0.006 gram/liter tends to nullify the brightness al though a usable copper deposit results. One of the unusual features of the present discovery is the unexpected degree of brightening which results from the use of extremely minor quantities of tellurium and furthermore that these trace quantities produce even better results than the somewhat higher quantities.

The copper cyanide baths can be made up of copper cyanide and an alkali metal cyanide with or without the addition of an alkali metal hydroxide or carbonate, and with or without the addition of tartrates, glycolates, or gluconates, citrates, malates or other similar organic acids or their salts, though the preferred baths contain such salts of these organic acids.

As examples of representative copper cyanide baths to which additions of traces of tellurium compounds can be made to elfect fine-grained bright deposits, the following formulations are listed, though wide variations of the composition of these baths can be made without loss of the brightening action caused by the trace of tellurium compound (added preferably in the tellurite form). It is to be understood that replenishment additions of tellurium compound must be made to replace that lost during the electrodeposition process. Even though the tel lurium is present in practically trace concentrations it is quite surprising how comparatively slowly it is depleted from the baths during electrodeposition.

Example II Oz./gal Grams/liter Copper cyanide 6.0 45 Potassium cyanide 9. 7 72. Potassium hydroxide- 2.0 15 Rochelle salts 6. 0 45 Tellurium 0. 0002-0. 006

(average 0.003)

Example III OzJgal Grams/liter Copper cyanide 3. 5 25. 2 Sodium cyanide 4. 7 35. 2 Potassium hydroxide 2. 5 18. 75 Potassium or Sodium glycolate 4-6 30-45 Tellurium s 0. 0002-0. 006

In Example III, the glycolate may be replaced by tartrate, gluconate or citrates in equivalent quantities, with glycolates, tartrates and citrates being somewhat superior to gluconates. v

The copper cyanide baths are preferred to be operated warm with optimum results at temperatures of 50 C.- (3., though cooler or warmer baths may be used with excellent results. It is preferred to use the baths of composition similar to the above examples, operated at maximum current densities under given conditions of temperature and agitation. However, satisfactory results are obtained when the copper cyanide varies between about 3 to about 12 ounces per gallon, the alkali metal cyanide varies between about 4.5 to about 20 ozs./gal., and the alkali metal hydroxide varies between about /2 to about 4 ozs./gal. of the bath. Under the usual commercial operation, cathode current densities of 10-60 amperes per square foot are used, and preferably the cathode efliciency should be less than 100% for the maximum brightness and widest bright plating range. By varying the concentration and the ratio of free cyanide to copper metal, as is well-known in the art, it is a simple matter to obtain maximum brightness and wide bright plate with any given copper cyanide bath, as: long as the tellurium is present in the concentration of about 0.0002 to 0.006 gram per liter.

Small concentrations of dissolved lead (0.0020.01 gram per liter) may be used as an auxiliary brightener, though in general it is not needed with the tellurium brightener, where pitting is seldom encountered. Thus, the tellurium additive makes possible a very simple bright, fine-grained copper plating bath. In examples of copper cyanide baths such as I, II and Ill, carbonates, glycolates, gluconates, citrates, etc., may also be present, also mixtures of sodium, potassium, and lithium salts. The baths may be operated at room temperatures up to at least C., and the current densities may be from a few amperes per square foot to at least sixty amperes per square foot depending on the temperature and concentration of the bath and the degree of agitation. Interrupted current or periodic current reversal may be used.

The traces of tellurium that cause the fine-grained bright plate do not affect the adhesion of the plate to the underlying metal such as steel, brass, copper, zinc or aluminum, nor the adhesion of any over-lay plate on the copper plate.

The brightness of the resulting copper plate is enhanced to an unexpected degree by using in conjunction with the above disclosed quantities of tellurium, certain anionic wetting agents and dispersing agents in controlled quan tities in the bath. A unique cooperation between the tellurium and these specific wetting agents or dispersing Patented July 1, 1958 us i i scan SOsHJ or multiples of this grouping in which n is usually about 1 to 100, and nuclear sulfonated polystyrene in the form of .a sodium, potassium or ammonium salt and having the repeating grouping S0311 SOaH n where n is usually about 1 to 100. The naphthalene suifonic acid salt is commercially available under the designation Daxad #11 from Dewey & Almy Co. and is understood to be a polymerized product which is prepared by condensing alpha or beta naphthalene sulfonic acid with formaldehyde in accordance with the reacting conditions described in U. S. Patent No. 2,028,482. The nuclear sulfonated polystyrene salt is available under the trade designation Lustrex X-710C from the Monsanto Chemical Company. Enhanced brightening in the tellurium containing cyanide copper baths of this invention is obtained when about 0.1 gram/liter to about 5.0 grams/liter of the above anionic wetting agents or dispersing agents are employed. If desired, mixtures of one or more of these wetting or dispersing agents may be used in approximately similar concentrations. The following examples illustrate in greater detail preferred bath compositions including tellurium in conjunction with such anionic wetting agents or dispersing agents.

Example IV Grams/ liter Copper cyanide 45 Sodium cyanide 56.5 Potassium hydroxide 18.75 Potassium tartrate 30 Tellurium 00002-0006 Sodium decyl ether sulfate .25-5

Example V Grams/liter Copper cyanide 45 Sodium cyanide 56.5 Potassium hydroxide 18.75 Potassium tartr ate 30 Tellurium 00002-0006 Mixture of sodium decyl ether sulfate and sodium dodecyl ether sulfate W .25-5

Example VI Grams/ liter Copper cyanide 45 Sodium cyanide 56.5 Potassium hydroxide 18.75 Potassium tartrate 30 Tellurium 00002-0006 Sodium decyl ether sulfate .25-5 Methylene bis (alpha naphthalene sulfonic acid) 0.1-5

1 Daxa'd #11 .(Dewey &-Almy 00;).

Example VI Grams/liter Copper cyanide 45 Sodium cyanide 56.5 Potassium hydroxide 18.75 Potassium tartrate 30 Tellurium 00002-0006 Sodium decyl ether sulfate .25-5 Nuclear sulfonated polystyrene 1 0.1-5

Lusti'ex X-710C (Monsanto Chemical 00.).

Example VIII Grams/liter Copper cyanide 45 Sodium cyanide 56.5 Potassium hydroxide 18.75 Potassium tartrate '30 Tellurium 0.0002-0006 Methylene bis (alpha naphthalene sulfonic acid) 0.1-5

Daxad #11 (Dewey & Almy 00.).

Example IX Grams/liter Copper cyanide 45 Sodium cyanide 56.5 Potassium hydroxide 18.75 Potassium 'tartrate 30 Tellurium 0.0002-0006 Nuclear sulfonated polystyrene 0.1-5

Lustrex'X-71OC (Monsanto Chemical Co.).

The baths of Examples IV-IX when operated under the'general conditions set forth in connection with the baths of Examples I-III produce unusually bright copper deposits. The cooperation between the tellurium and these auxiliary agents was unexpected since no enhancement of brightening was obtained from the incorporation of these same auxiliary agents .in comparable cyanide copper baths in the absence of the above specified quantities of tellurium.

The dispersing agents described above are preferred for the purposes of this invention because they are somewhat more stable in the bath than the anionic Wetting agents. It is believed that these dispersing agents function to produce the enhanced brightening because they include benzene or naphthalene rings which are linked by methylene or ethylene groups, the rings being .sulfonated. Compounds containing these repeating groupings apparently are sufliciently stable to resist the breakdown influences which exist in the bath. Free lauryl or other fatty alcohols which are sometimes present as impurities in surface-active agents such as sodium lauryl sulfate have been found to dull the resulting plate and therefore it is preferred to employ only the purest obtainable grades of the surface-active agents hereinabove disclosed.

The useof arsenicalone in an alkaline cyanide copper bath gives some brightening of the copper plate, but arsenic has the fault that it causes dulling of the plate in low current density ranges, especially causing dulling in recesses.

It has been found that in cyanide copper baths containing arsenic the use of tellurium in the small amounts above indicated overcomes the dulling normally resulting from the arsenic and makes the recesses bright. The combination of arsenic and tellurium increases the overall brightness of the resultant plate.

It is preferred to addthe arsenic .to the bath as sodium arscnite (Na AsO or arsenious acid (As O Sodium arsenate (Na AsO or arsenic oxides are not as bene- Jticial as the trivalent arsenic. Arsenic may be added to the copper anodes as such if desired. The trivalent form of arsenic is the preferred form in the bath. I

Arsenic (calculated as metal) may be .present in the bath in concentrations of about 0.01 to 1 gram/liter, and preferably about 0.05 to 0.4 gram/liter.

This application is a continuation-in-part of my co'- pending application, Serial No. 479,851, filed January 4, 1955, which application is now abandoned.

What is claimed is:

1. A plating bath comprising an alkaline copper cyanide bath containing in solution tellurium in an amount in the range of about 0.0002 to about 0.006 gram/liter.

2. A plating bath comprising an alkaline copper bath containing about 3-12 ounces of copper cyanide, about 4.5- ounces of alkali metal cyanide, about .5 to about 4 ounces of alkali metal hydroxide, about 4-8 ounces of a salt selected from the group consisting of alkali metal tartrates, glycolates, malates, glue-snares and citrates, sufficient Water to make up a gallon of bath, and an amount of tellurium in the range of about 0.0002 to about 0.006 gram/liter in solution in said bath.

3. A plating bath comprising an alkaline copper cyanide bath containing 3-4 ounces of copper cyanide, 4.5-5 ounces of alkali metal cyanide, about .5 ounces alkali metal hydroxide, about 4 ounces Rochelle salts, suflicient Water to make up a gallon of bath, and in solution 0.0002 to 0.006 gram/liter of tellurium.

4. A bath in accordance with claim 2 containing in addition thereto about 0.1-5.0 grams/liter of at least; one material containing the repeating grouping where n is a whole number.

5. The method of electrodepositing fine grained, lustrons copper plate which comprises the step of electrodepositing copper from an alkaline cyanide copper hath containing in solution tellurium in an amount in the range of about 0.0002 to about 0.006 gram/liter.

6. The method of electrodepositing fine grained, lustrous copper plate which comprises the step of electrodepositing copper from an alkaline cyanide copper bath containing in solution about 3-12 ounces of copper cyanide, about 4.5-20 ounces of alkali metal cyanide, about .5 to about 4 ounces of alkali metal hydroxide, about 4-8 ounces of a salt selected from the group consisting of alkali metal tartrates, glycolates, malates, gluconates and citrates, sufiicient water to make up a gallon of bath, and an amount of tellurium in the range of about 0.0002 to about 0.006 gram/liter in solution in said bath.

7. The method of electrodepositing fine grained, lustrous copper plate which comprises the step of electrodepositing copper from an alkaline cyanide copper bath containing in solution about 3-4 ounces of copper cyanide, 4.5-5 ounces of alkali metal cyanide, about .5 ounce alkali metal hydroxide, about 4 ounces Rochelle salts, suficient water to make up a gallon of bath, and in solution 0.0002 to 0.006 gram/liter of tellurium.

8. A method in accordance With claim 6 wherein the solution contains in addition thereto about 0.1-5.0 grams/ liter of a least one material selected from the group con sisting of surfaces of 8-18 carbon atom normal primary alcohols, sulfated monoethylene glycol ethers of 8-18 carbon atom normal primary alcohols, water soluble salts of methylene bis (alpha naphthalene sulfonic acid) and water soluble salts of nuclear sultonated polystyrene.

9. A method in accordance with claim 6 wherein the gum...

where n is a whole number.

10. A plating bath in accordance with claim 2 containing in addition. thereto about 0.1-5.0 grams/liter of at least one material selected from the group consisting of sulfates of 8-18 carbon atom normal primary alcohols, sulfated monoethylene glycol ethers of 8-18 car bon atom normal primary alcohols, Water soluble salts of methylene bis (alpha naphthalene sulfonic acid) and water soluble salts of nuclear sulfonated polystyrene.

11. A bath in accordance with claim 1 containing .in addition thereto arsenic in an amount of about 0.01 to 1 gram/liter.

12. A plating bath comprising an alkaline copper cyanide bath containing in solution tellurium in an amount in the range of about 0.0002 to about 0.006 gram/liter, said tellurium being introduced in the said bath in the form of tellurium dioxide and its salts.

13. A bath in accordance with claim 2 containing in addition thereto about 0. 1-5 .0 grams/liter of at least. one material containing the repeating grouping where n is a whole number.

14. A method in accordance With claim 6 wherein the solution contains in addition thereto about 0.1-5.0 grams/liter of at least one material containing the re peating grouping Where n is a whole number.

15. A method in accordance with claim 6 wherein the solution contains in addition thereto about 0.1 to 5.0 grams/liter of at least one sulfate of 8-18 carbon atom normal primary alcohols.

16. A method in accordance with claim 6 wherein the solution contains in addition thereto about 0.1 to 5.0 grams per liter of at least one sulfated monoethylene glycol ether of 8-18 carbon atom normal primary alcohols.

References Cited in the file of this patent UNITED STATES PATENTS 1,863,869 McCullough et al June 21, 1932 2,216,605 Sklarew et a1. 'Oct. 1, 1940 2,612,469 Reisinger Sept. 30, 1952 2,677,654 Chester et a1. May 4, 1954 2,689,216 Nevers et a1 a- Sept. 14, 1954 2,701,234 Wernlund Feb. 1,

OTHER REFERENCES Ser. No. 351,241, Weiner (A. P. C.), published May 18, 1943.

UNITED STATES PATENT OFFICE CERTIFICATE OF CUEGTION Patent Non 2,841,542 July 1, 1958 John W; Manc uen It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and "that the said Letters Patent should read as corrected below.

Column 5, line 63, for "surfaces" read. sulfates o Signed and sealed "this 25th day of November 1958",

(SEAL) Attest:

KARL Ho AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents 

1. A PLATING BATH COMPRISING AN ALKALINE COPPER CYANIDE BATH CONTAINING IN SOLUTION TELLURIUM IN AN AMOUNT IN THE RANGE OF ABOUT 0.0002 TO ABOUT 0.006 GRAM/LITER. 